Wednesday, June 19, 2013

US Study Reveals Autism Linked to Toxins and Pollution

US kids born in polluted areas more likely to have autism.

Women who live in areas with polluted air are up to twice as likely to have an autistic child than those living in communities with cleaner air, according to a new study. Building on two other smaller, regional studies, the Harvard University research is the first to link air pollution nationwide with autism. It also is the first to suggest that baby boys may be more at risk for autism disorders when their mothers breathe polluted air during pregnancy. Babies born in areas with high airborne levels of mercury, diesel exhaust, lead, manganese, nickel and methylene chloride were more likely to have autism than those in areas with lower pollution. The strongest links were for diesel exhaust and mercury.

Building on two smaller, regional studies, the Harvard University research is the first to link air pollution nationwide with autism. It also is the first to suggest that baby boys may be more at risk for autism disorders when their mothers breathe polluted air during pregnancy.

Babies born in areas of the United States with high airborne levels of mercury, diesel exhaust, lead, manganese, nickel and methylene chloride were more likely to have autism than those in areas with lower pollution. The strongest links were for diesel exhaust and mercury.

“The striking similarity with our results and the previous studies adds a tremendous amount to the weight of evidence that pollutants in the air might be causing autism in children,” said Andrea Roberts, a research associate at the Harvard University School of Public Health and lead author of the new study published online in Environmental Health Perspectives.

Scientists have been trying to figure out whether a variety of environmental exposures are linked to autism, a neurological disorder diagnosed in one out of every 50 U.S. children between the ages of 6 and 17.

Because the new air pollution study has some weaknesses, however, its findings, while interesting, are not conclusive, several scientists said. For example, the researchers estimated the mothers’ exposure to air pollutants based on computer models.

“It’s the same weakness as other studies [on environmental pollutants and autism]. They’re using an EPA model, which estimates what’s coming out of factories and traffic and spits out a pollution estimate,” said Amy Kalkbrenner, an assistant professor of epidemiology at the University of Wisconsin-Milwaukee, who was not involved in this study.

Also pollution varies by season and “pregnant women don’t just sit inside a census tract,” said Kalkbrenner, who conducted a similar, smaller study in 2010.

In addition, the results may be skewed because children in urban areas have more access to doctors and clinics where they are more likely to be diagnosed, said Irva Hertz-Picciotto, an environmental epidemiologist at the University of California, Davis, who studies autism.

The new study used information from 325 mothers, all nurses from around the country, who gave birth after 1987 to a child later diagnosed with autism. The researchers divided these children into five groups based on their mothers’ estimated air pollution exposure during pregnancy and compared their autism rates to 22,000 non-autistic children born from 1987 to 2002. The U.S. Environmental Protection Agency's pollution estimates were broken down by census tract. The income and education level of the families were factored in, since they also can be linked to air pollution.

Researchers used U.S. EPA models that estimate air pollution based on traffic and industrial emissions.

For mercury and diesel, the mothers in the highest exposure group were twice as likely to have an autistic child. Lead, manganese, nickel, methylene chloride and overall metal exposure also were associated with higher incidences of autism. Twenty-six of 180 pollutants had a significant association between exposure and autism rates.

“Since so many [pollutants] were linked to higher autism rates, we can’t tell from the study which ones might be the causes,” Roberts said.